In modern flight decks, the primary flight information display (PFD) and the navigation display (ND) are the key displays available for providing situational awareness to the pilot. Although the primary flight information display provides aircraft attitude and performance information through the attitude direction indicator (ADI), airspeed tape, heading and track indicator, and vertical speed indicator (VSI), the performance information is not shown in relation to the aircraft's surroundings. The navigation display provides fairly complete horizontal situational awareness with a top down (map) view of the aircraft and its surroundings. The navigation display tries to address vertical situational awareness through a vertical path deviation indicator, waypoint altitude constraint information, a range to altitude arc, and a selectable terrain picture from a Terrain Awareness and Warning Systems (TAWS). TAWS provides a contour map of surrounding terrain. Due to the display shading limitations and the nature of a top down view display, the contour map can only provide a general awareness of the surrounding terrain height. Also, to avoid pilot complacency and possible false alarms on takeoff and landing, some systems may have a “blackout” elevation below which the display provides no terrain information in normal conditions. Even with these vertical situational awareness features on the navigation display, the information still requires some interpretation, and approach and landing accidents continue to occur. This leaves the pilot with TAWS to provide both horizontal and vertical situational awareness of terrain. The pilot may not be able to perform an optimal vertical maneuver if the pilot is not aware of the height of the surrounding terrain.
For flight deck displays that show the terrain directly in front of the aircraft, the input for this type of device may be a database of topography information that generates a display based on position information from the aircraft's navigational equipment. However, the display changes with slight adjustments to the direction of the aircraft, making it appear “noisy”. Also, navigational instruments for determining the exact position of an aircraft usually have some degree of error. For example, if the aircraft's automated navigational equipment is only accurate to within 10 nautical miles of the exact location of the aircraft, and the topography display only shows a “line” of topography directly in front of where the aircraft instruments indicate the aircraft is located, the topography display will be not be accurate as to the topography directly in front of the aircraft if the aircraft's exact position is actually 9.5 nautical miles from the location indicated by the navigation equipment. A presentation of terrain and waypoints along the current track of the aircraft provides some awareness, but during turns the pilot will not see terrain in the projected path of the turn.
To assist pilots with final approach and landing, a localizer and a glideslope indicator may be provided on the electronic attitude director indicator to give the pilot information as to how much the aircraft is deviating from the ideal landing approach angle, as defined by a radio signal from the runway. When the aircraft is not on this ideal path, the flight deck instruments do not indicate the degree of correction required to return the aircraft to the correct descent path. If the pilot under- or overcorrects the descent angle and cannot position the aircraft onto a suitable landing approach path in a short period of time, the pilot may have to make a decision to abort the landing, circle, and begin another landing approach. A system that gives the pilot better information about the current relationship between the aircraft and the ideal descent and landing approach path will aid the pilot.
At various times during ascent and descent of an aircraft, it may be necessary for the aircraft to reach a target speed by the time the aircraft reaches a particular geographic point. The airspeed tape on the primary flight information display indicates current and selected airspeeds, but the pilot has to judge how long it will take to achieve the selected airspeed. The pilot then needs to calculate how far the aircraft will travel before the target speed is achieved. These calculations and estimations may not be very precise and may distract the pilot from performing other duties connected with flying the aircraft and maintaining an accurate mental picture of the situation.
For many of the flight information displays in the cockpit, the reference mark by which the instrument is read is either fixed with a moving scale to indicate the value of parameter (for example, an altimeter tape) or the reference mark moves with respect to a fixed scale (for example, a vertical speed indicator). If the reference aircraft symbol on a vertical profile display (VPD) is fixed near the bottom of the display and the aircraft is in a descent, the resolution of the display for that range of altitudes will be insufficient to provide the pilot with any increased awareness of the terrain the aircraft is approaching. Similarly if the aircraft symbol is fixed at the top of the display and the aircraft is climbing, resolution will be insufficient to increase the pilot's awareness of the airplane's relationship with the terrain ahead.
One known type of vertical display provides a terrain picture for the navigation displays, EHSIs, and standalone weather radar display units. Another known vertical profile display depicts the flight plan in an along flight plan presentation. The waypoints are positioned relative to each other and not on an absolute scale (For example, if waypoint A is at FL390 and waypoint B has an altitude constraint of FL410, then waypoint A will be at a position on the display lower than waypoint B, but otherwise the vertical position of the points will not correlate to any absolute scale). A display that provides better vertical flight situation awareness to the pilot would be desirable.